Document: JOH-3-59-33

Greenhouse gas emissions from drainage waters in an intensively farmed, subtropical valley.

HARRISON, J.A.* and P.A.MATSON

Stanford University, Stanford, CA, USA ¹

Abstract:

The production and emission of nitrous oxide (N₂O), methane (CH₄), and carbon dioxide (CO₂) from surface waters draining agricultural regions is not well understood, especially in non-temperate regions where the most rapid agricultural intensification is currently occurring. We measured the rates and patterns of N₂O, CH₄, and CO₂ emissions from freshwater drainage systems and estuaries receiving agricultural and mixed agricultural/urban drainage water from the intensively farmed Yaqui Valley of Sonora, Mexico. N₂O emissions in both pure agriculture and mixed urban/agriculture drainage systems were high (means: 4.02-23.5 ng N₂O-N cm^-2 hr^-1) with N₂O emissions increasing as much as 600% following a valley-wide fertilization/irrigation event. Flux measurements along estuarine transects revealed that N₂O production is sustained above levels predicted by dilution calculations, suggesting that N₂O production is not limited by dissolved inorganic nitrogen in the drainage system. Rates of CO₂ and CH₄ emission varied dramatically over the course of a growing season (0.81-20.46 g CO₂ cm^-2 hr^-1, and 0.37-4911.53 g CH₄ cm^-2 hr^-1respectively), and there was a clear trend toward increasing CO₂ emissions over the two months following irrigation. CH₄ emissions were greater in the freshwater drainage and estuary (mean flux: 799.92 g CH₄ cm^-2 hr^-1) receiving mixed agricultural-urban drainage than in the freshwater drainage and estuary receiving purely agricultural drainage (mean flux: 113.21 g CH₄ cm^-2 hr^-1). Our results show that N₂O emissions from drainage waters in the Yaqui Valley are high, and indicate that rates of greenhouse gas emissions from surface drainage waters are tightly linked to upland development and management practices.

Keywords: land-water interaction, greenhouse gas, trace gas, nitrous oxide, methane, carbon dioxide, agriculture, subtropics

This abstract is being presented at: 2:15 PM in session:
Oral Session #31: Agroecology.